Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Slender annuals, to 30 cm tall; stems erect, branching above, striate (having longitudinal stripes), usually nearly hairless. Leaves: Opposite, at least below the inflorescence; blades 15-50 mm long, once or twice pinnately lobed, the lobes linear to filiform, or rarely lanceolate, upper and lower surface glabrous. Flowers: Flower heads small, yellow, and radiate, though the rays are small and inconspicuous; heads borne singly or in loose, cymose arrays; involucre narrowly campanulate to subcylindric, 5-6 mm high and 3-4 mm wide, the bracts (phyllaries) in 2 distinct series; outer phyllaries 3-5 per flower head, narrow (linear to lanceolate) and green, sometimes with a few gland-tipped teeth on the margins; inner phyllaries wider (ovate), straw-colored, and striate with 10-15 dark-colored nerves; paleae (bracts on the receptacle that subtend each floret) appearing similar to the inner phyllaries, with dark colored striations and apiculate tips; ray florets 1-3 per flower head, the laminae (ray petals) 1-2 mm long, pale yellow to orange; disc florets 3-10 perflower head, yellow. Fruits: Achenes from ray and disc florets have different morphology; ray achenes are oval-shaped and winged, 3-5 mm long and reddish brown; disc achenes are narrower, up to 14 mm long, and topped with a pair of awns. Ecology: Found on open rocky slopes, often on igneous and calcareous soils, from 3,000-8,500 ft (914-2591 m); flowers June-October. Distribution: AZ to TX; south to MEX Notes: With its 2-barbed achenes, this species could easily be mistaken for Bidens. Get your hand lens and look at the phyllaries; H. pinnatum has 2 obviously different types. The outer layer consists of only a few narrow green bracts. The inner phyllaries look the same as the recepticular bracts; they are oval shaped, light-colored, and have numerous dark nerves. The other characteristic that distinguishes this species is the dimorphic achenes. Ray achenes are oval-shaped, while the disc achenes are narrow and 2-barbed. Ethnobotany: Unknown Etymology: Heterosperma comes from Greek heteros, different and sperma, seed, referring to the dimorphic achenes; pinnatum means pinnate, referring to the leaf morphology. Synonyms: None Editor: SBuckley 2010, AHazelton 2017